The function sdk_wifi_softap_start is one of two paths that allocates a struct netif and also accesses the netif->hwaddr so is needed for lwip development. This function depends on static data and functions so a good bit so other code was needed.
* wifi_set_sleep_type returns a bool success flag.
* wifi_get_sleep_type seemed useless, just returning an argument. Added an implementation using sdk_pm_get_sleep_type.
Fixes#147
* Can vary tick rate from 100Hz via configTICK_RATE_HZ. Note that the
SDK binary libraries are hard-coded to assume the tick rate is 100Hz,
so changing the tick rate may have unexpected consequences for lower
layer WiFi behaviour (such as certain kinds of timeouts happening
faster/slower.)
* Setting configCPU_CLOCK_HZ to 160MHz means ESP will set 160MHz during
initialisation. Only 80MHz and 160MHz are supported.
* Timing of tasks is no longer affected by current CPU freq (whether set
via configCPU_CLOCK_HZ or via sdk_system_update_cpu_freq().)
Previously doubling the CPU frequency would double the tick rate.
